If you truly believe that the stock isn't worth 50B, you are free to short the stock. In fact, lots of people out there are shorting the stock. However there is no smoke and mirrors here: they release quarterly financials, they've been public for a boom time and a down time. The aggregate of the market disagrees with your view.

The OP also specifically says the point of the charade is to "make huge amounts of money for the founder and the initial VCs". Uber/Doordash didn't just make huge amounts of money for the founders and initial VCs, it made huge amounts of money for early employees, later employees, current employees, the initial VCs, the later VCs. People have had years to exit their positions and unlimited liquidity to do so... some other rational actor was happy to buy the shares they were selling. If you say these companies are charades than so is every publicly traded company.

Most companies have made a ton of money for anyone who bought in April-June 2020 and sold by September-November 2021. I personally made > 2x on certain stocks during these 20-22 months.

UBER currently trades at $27, well below its IPO price of $42 in May 2019, and we had pretty noticeable inflation in the meantime. So how have they made money for early investors and employees is not much of a charade: by selling to a greater fool :(

The standard advice here is that you shouldn’t expect that you can remain solvent longer than the markets can remain irrational. Uber certainly has a questionable potential to ever make a reasonable amount of money but I can’t really see that causing a significant drop in stock price any year soon. Everyone paying attention invested in Uber in its current difficult to profit state and I can’t think of a reason they’ll suddenly have a dramatic change of heart.